1- Go to Appearance – Theme Options and select Entry settings tab
2- Scroll down and check the box:Use excerpt summary post and Enable featured thumbnail
3- Setup the Width and Height for the post thumbnail

Recommended Featured Image size is 780px (width) x 480px (height) and above

4- Click Save settings

Once you updated the Featured Image size, kindly make sure to Regenerate Thumbnails your Featured Image size.

Setup Blog Categories Widget

This will show a row of all the blog categories on top of the page (below newsletter section).
1- Go to Appearance – Widgets
2- Drag Categories widget to Blog Categories Widgets